THE BLOOD AND ITS CIRCULATION 67 



which soaks through the capillaries, and so some always 

 surrounds the cells. White blood cells also go through the 

 sides of the capillaries and live between the cells of the 

 body. Each cell also gives off waste matter. The mix- 

 ture of these matters makes a fluid called lympk, which is 

 always bathing the cells. Lymph is thin blood without 

 its red cells. Only a little lymph can go back to the 

 capillaries ; so to take away the rest there is another set 

 of tubes called lymphatics. 



124. Lymphatics. Each lymphatic is like a small capil- 

 lary with thin walls. It begins in spaces between the 

 cells and carries away the lymph, just as a pump driven 

 deep into the wet earth brings up water. The smaller 

 lymphatics unite to form about twenty fine tubes for each 

 limb. They are too small and thin to be easily seen. 

 They run up the limb, and at the backbone join together 

 to form a single tube about the size of a quill. This tube 

 is called the thoracic duct. It opens into a large vein in 

 the neck. Thus the matters which leak out of the capil- 

 laries return to the blood in a roundabout way. Digested 

 fat also reaches the blood through the lymphatics. The 

 lymphatics are really a third set of blood tubes. 



125. Lymph nodes. Here and there the lymphatics 

 pass through little bodies like grains of wheat or corn. 

 They can be felt under the lower jaw and in the groin, 

 and are called lymph nodes. Each node is like a sponge 

 filled with white blood cells. As the lymph flows through 

 the nodes they strain out and keep back poisons and waste 

 matters which the white blood cells eat and destroy. So 

 these nodes protect the body against poisoning. In some 

 diseases they get so full of poison that they become 

 swollen, red, and painful. In scrofula the nodes in the 

 neck often form large swellings from this cause. 



